csr | R Documentation |
Generate completely spatially random points on a polygon.
csr(poly,npoints)
poly |
A polygon data set. |
npoints |
The number of points to generate. |
csr
generates points randomly in the bounding box of poly,
then uses
pip
to extract those in the polygon. If the number of points remaining is
less than that required, csr
generates some more points in the
bounding box until at least npoints
remain inside the polygon. If too many
points are generated then the list of points is truncated.
Uses runif()
to generate random numbers and so updates .Random.seed
,
the standard S random number generator seed.
A point data set consisting of npoints
points distributed randomly,
i.e. as an independent random sample from the uniform distribution
in the polygon defined by poly
.
Rowlingson, B. and Diggle, P. 1993 Splancs: spatial point pattern analysis code in S-Plus. Computers and Geosciences, 19, 627-655; the original sources can be accessed at: https://www.maths.lancs.ac.uk/~rowlings/Splancs/. See also Bivand, R. and Gebhardt, A. 2000 Implementing functions for spatial statistical analysis using the R language. Journal of Geographical Systems, 2, 307-317.
data(cardiff)
nsim <- 29
emp.Ghat <- Ghat(as.points(cardiff), seq(0,30,1))
av.Ghat <- numeric(length(emp.Ghat))
U.Ghat <- numeric(length(emp.Ghat))
L.Ghat <- numeric(length(emp.Ghat))
U.Ghat <- -99999
L.Ghat <- 99999
for(i in 1:nsim) {
S.Ghat <- Ghat(csr(cardiff$poly, length(cardiff$x)), seq(0,30,1))
av.Ghat <- av.Ghat + S.Ghat
L.Ghat <- pmin(S.Ghat, L.Ghat)
U.Ghat <- pmax(S.Ghat, U.Ghat)
}
av.Ghat <- av.Ghat/nsim
plot(av.Ghat, emp.Ghat, type="l", xlim=c(0,1), ylim=c(0,1),
xlab="Simulated average G", ylab="Empirical G")
lines(c(0,1),c(0,1),lty=2)
lines(U.Ghat,emp.Ghat,lty=3)
lines(L.Ghat,emp.Ghat,lty=3)
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